1. Field of the Invention
The present invention relates to a pixel, an organic light emitting display, and a method for driving the organic light emitting display including the pixel.
2. Discussion of Related Art
Recently, various flat panel displays having advantages such as reduced weight and volume over cathode ray tubes (CRT) displays have been developed. Flat panel displays include liquid crystal displays (LCD), field emission displays (FED), plasma display panels (PDP), and organic light emitting displays.
Among the flat panel displays, the organic light emitting displays make use of organic light emitting diodes that emit light by re-combination of electrons and holes. The organic light emitting display has advantages such as high response speed and low power consumption.
FIG. 1 is a circuit diagram showing a pixel 4 of a conventional organic light emitting display.
With reference to FIG. 1, the pixel 4 of a conventional organic light emitting display includes an organic light emitting diode (OLED) and a pixel circuit 2. The pixel circuit 2 is coupled to a data line Dm and a scan line Sn, and controls light emission of the organic light emitting diode (OLED).
An anode electrode of the organic light emitting diode (OLED) is coupled to a pixel circuit 2, and a cathode electrode thereof is coupled to a second power supply ELVSS. The organic light emitting diode (OLED) generates light of a predetermined luminance corresponding to an electric current from the pixel circuit 2.
When a scan signal is supplied to the scan line Sn, the pixel circuit 2 controls the amount of electric current provided to the organic light emitting diode (OLED). The amount of current corresponds to a data signal provided to the data line Dm. The pixel circuit 2 includes a second transistor M2, a first transistor M1, and a storage capacitor Cst. The second transistor M2 is coupled to a first power supply ELVDD and the organic light emitting diode (OLED). The first transistor M1 is coupled between the data line Dm and the scan line Sn. The storage capacitor Cst is coupled between a gate electrode and a first electrode of the second transistor M2.
A gate electrode of the first transistor M1 is coupled to the scan line Sn, and a first electrode thereof is coupled to the data line Dm. A second electrode of the first transistor M1 is coupled with one terminal of the storage capacitor Cst. The first electrode can be either a source electrode or a drain electrode, and the second electrode is the other one of the source electrode or the drain electrode. For example, when the first electrode is the source electrode, the second electrode is the drain electrode. When a scan signal is supplied to the first transistor M1 coupled with the scan line Sn and the data line Dm, the first transistor M1 is turned-on to provide a data signal from the data line Dm to the storage capacitor Cst. At this time, the storage capacitor Cst is charged with a voltage corresponding to the data signal.
The gate electrode of the second transistor M2 is coupled to one terminal of the storage capacitor Cst, and a first electrode thereof is coupled to another terminal of the storage capacitor Cst and a first power supply ELVDD. Further, a second electrode of the second transistor M2 is coupled with the anode electrode of the organic light emitting diode (OLED). The second transistor M2 controls the amount of electric current flowing from the first power supply ELVDD to a second power supply ELVSS through the organic light emitting diode such that the current corresponds to the voltage charged in the storage capacitor Cst. At this time, the organic light emitting diode (OLED) emits light corresponding to the amount of electric current supplied from the second transistor M2.
However, the pixel 4 of the conventional organic light emitting display may not display an image of substantially uniform luminance. Threshold voltages of the second transistors M2 (drive transistors) in the pixels 4 vary according to process deviations during fabrication. When the threshold voltages of the second transistors M2 vary, although data signals corresponding to the same luminance are supplied to the pixels 4, the organic light emitting diodes (OLEDs) emit light of different luminance due to variations in the threshold voltages of the second transistors M2.